Types in tea

To understand how types are handled in tea, we recommend to first complete the Custom printer app exercise. When you do it, you may notice something interesting: we get a float variable “pt” from the branch, but what if it was a different type, let’s say int?

Let’s break it

Well, let’s see what would happen if we changed float to int in this example:

int pt = muon->Get("pt");

Recompile and run the example:

cd build
make -j install
cd ../bin
./ttZ_analysis_print_events ttZ_analysis_print_events_config.py

As you see, it actually compiled (which is rather unexpected), however it throws and exception when you try to run it.

Multitype

The problem is that we don’t want to have different methods for different types, like GetInt(...), GetFloat(...), etc. Since C++ doesn’t allow overloading methods only based on return type, we use a little workaround:

• Get(...) returns a Schrödinger’s object that doesn’t know what type it is.
• When we assign it to a variable of a specific type, it calls the corresponding cast operator.
• The cast operator checks the actual branch type and either returns the value or throws an exception.

Bottom line

You can access a variable of any type through Get(...), but you have to know its type beforehand. Alternatively, you can use GetAs<some_type>(...) to cast it to another type, if you’re sure you know what you’re doing.